Although microbial life might survive the extreme conditions of space, for Homo sapien sapiens the space environment remains remarkably dangerous to life. One space life scientist, Vadim Rygalov, remarked that ensuring human life during spaceflight was largely about providing the basics of human physiological needs. From the most critical—meaning that its absence would cause immediate death, to the least critical—these include such constants available here on Earth of atmospheric pressure, breathable oxygen, temperature, drinking water, food, gravitational pull on physical systems, radiation mitigation, and others of a less immediate nature.

As technologies, and knowledge about them, stand at this time, humans are able to venture into space for short periods of less than a year only by supplying all of these needs either by taking them with them (oxygen, food, air, etc.) or creating them artificially (pressurized vehicles, centrifugal force to substitute for gravity). Spaceflight would be much easier if humans could go into a hibernation during the extremes of spaceflight, as had been demonstrated by certain types of microorganisms. It is because of the biomedical issues that challenge human spaceflight that I have to question trips to Mars, and returns, until we have tackled a lot of questions not even fully conceptualized as yet.

Resolving biomedical challenges proved difficult but not insurmountable for such basic spaceflight activities as those undertaken during the heroic age of space exploration when the United States and the Soviet Union raced to the Moon. Overcoming the technological hurdles encountered during the Mercury, Gemini, and Apollo programs were child’s play in comparison to the threat to human life posed by long duration, deep space missions to such places as Mars.

Even the most sophisticated of those, the lunar landings of Project Apollo, were relatively short camping trips on another body in the solar system, and like most camping trips undertaken by Americans the astronauts took with them everything they would need to use while there. This approach will continue to work well until the destination is so far away that resupply from Earth becomes highly problematic if not impossible for any number of reasons.

There is no question that the U.S. could return to the Moon in a more dynamic and robust version of Apollo; it could also build a research station there and resupply it from Earth while rotating crews out on a regular basis. In this instance, the lunar research station might look something like a more sophisticated and difficult to support version of the Antarctic research stations. A difficult challenge, yes; but certainly it is something that could be accomplished with presently envisioned technologies. The real difficulty is that at the point a lunar research station becomes a colony profound changes to the manner in which humans interact with the environment beyond Earth must take place. Countermeasures for core challenges—gravity, radiation, particulates, and ancillary effects—provide serious challenges for humans engaged in space colonization.

A possible future in space, humans and robots on Mars, as envisioned by artist Pat Rawlings.

One avenue that NASA has pursued, but without overwhelming success, is the technology of closed loop life support systems. A longstanding objective has been to build a spacecraft that could produce air, recycle water, manage waste, maintain humidity, and suppress fires. “Closing the loop” on environmental life support systems is a major technology challenge affecting the progress of human spaceflight and one that has yet to be resolved.

In 1991, environmental scientists began an experiment to test the feasibility of supporting human beings in a closed environmental system. Funded at $150 million by Texas oil magnate Edward Bass, humans at Biosphere 2 in Arizona’s Santa Catalina Mountains sought to test technologies that might be useful for sustaining life on the Moon or Mars. Designers of the three-acre facility provided for the complete recycling of water, food, and waste. Biosphere 2’s failure as a self-contained “terrarium” supporting humans on Earth, much less one moving through the near-vacuum of space, was an eye-opener for those pursuing long-duration human spaceflight. The experiment ended badly and after 1994 no further human habitation took place. The goal of keeping people alive in an enclosed, self-contained environment whisking through space may be beyond human capabilities for many centuries.

No terrestrial explorers have ever had to contend with the all of the extremes of the space environment in their activities. For all of the other rigors of their environments, even those in quest of the poles have had breathable air, pressures that did not require suits to ensure their lives, and water/ice. Only those engaged in undersea exploration face similar difficulties of survival in such extreme conditions to which Homo sapien sapiens are ill-evolved.